The demolition expert says "support beams and tie girders". Beams (used to support floors) and girders (used to support other beams and portions of floors) are both horizontal structural members. They only carry the weight of the floor, furniture, and people. Columns, on the other hand, are major vertical structural members that carry the weight of the building- including the weight from the beams and girders tied to them. They are always fitted with explosives in order to demolish a building. He should have said "... columns and beams ...".
The boy killed in the explosion is Robbie Cuneo. When Lt. Van Buren formerly indicts Hank Chapel, she charges him in the death of Richard Cuneo.